Johnson Controls 340968-XIM-A-0108 GASE RATE - CUBIC FEET PER HOUR1, Checking Supply Air Cfm

TABLE 12: GASE RATE - CUBIC FEET PER HOUR1

SECONDS	SIZE OF TEST DIAL
FOR ONE
REV.	1/2 CU. FT.	1 CU. FT.
10	180	360
12	150	300
14	129	257
16	113	225
18	100	200
20	90	180
22	82	164
24	75	150
26	69	138
28	64	129
30	60	120
32	56	113
34	53	106
36	50	100
38	47	95
40	45	90
42	43	86
44	41	82
46	39	78
48	37	75
50	36	72
52	35	69
54	34	67
56	32	64
58	31	62
60	30	60

1.EXAMPLE: By actual measurement, it takes 38 seconds for the hand on the 1-cubic foot dial to make a revolution with just a 100,000 BTUH furnace running. Using this information, locate 38 seconds in the first column of Table 12. Read across to the column headed “1 Cubic Foot,” where you will see that 95 cubic feet of gas per hour are consumed by the furnace at that rate. Multiply 95 x 1050 (the BTU rating of the gas obtained from the local gas company). The result is 99,750 BTUH, which is close to the 100,000 BTUH rating of the furnace.

340968-XIM-A-0108

CHECKING SUPPLY AIR CFM

To check the supply air CFM after the initial balancing has been completed:

1.Remove the two ¼ inch dot plugs in the duct panel.

2.Insert at least 8 inches of ¼ inch tubing into each of these holes for sufficient penetration into the airflow on both sides of the indoor coil.

3.Using an inclined manometer, determine the pressure drop across the dry evaporator coil. Since the moisture on an evaporator coil may vary greatly, measuring the pressure drop across a wet coil under field conditions would be inaccurate. To ensure a dry coil, the compres- sors should be deactivated while the test is being run.

4.Knowing the pressure drop across a dry coil, the actual CFM through the unit can be determined from the curve in Coil Delta P vs. Supply Air CFM figure.

Failure to properly adjust the total system air quan- tity can result in extensive system damage.

After readings have been obtained, remove the tubes and reinstall the two ¼ inch plugs removed in Step 1.

De-energize the compressors before taking any test mea- surements to ensure a dry indoor coil.

18 Johnson Controls Unitary Products